1. Field
The present invention relates to electrolytic capacitors to be used in a variety of electronic devices, electric devices, industrial devices, and automotive devices. It also relates to a method of manufacturing the same capacitors.
2. Background Art
The electronic devices have adopted digital technology, so that the capacitors employed in output side circuits, e.g. a smoothing circuit or a control circuit, of the power supplies of those devices need to be smaller in size and greater in capacity. On top of that, the capacitor is desired to have a smaller equivalent series resistance (hereinafter simply referred to as ESR) in a high frequency band. A liquid impregnated capacitor that employs liquid electrolyte such as electrolyte solution has been typically used in the output side circuit of the power supply. However, in recent years, solid electrolytic capacitors have been used for the same purpose, and they employ solid electrolyte such as transition metal oxides such as manganese dioxide, organic semiconductor, e.g. TCNQ complex salt, or conductive polymer including polypyrrole, polythiophene, polyaniline. As discussed above, there is a trend toward smaller ESR in the electrolytic capacitors.
The solid electrolytic capacitor is excellent particularly in the smaller ESR than the liquid electrolytic capacitor; however, its recovery action is poor at a failure of anodic oxide film working as dielectric. The solid electrolytic capacitor thus tends to invite an increment in leakage current, and in the worst case, it results in a short.
On the other hand, audio-video devices and automotive electronics need increasingly a higher reliability, so that the solid electrolytic capacitor should improve the performance of small leakage current and also the anti-short properties in addition to the advantages of small in size, great in capacity, and low ESR. To meet those needs, a hybrid electrolytic capacitor has been proposed, namely, electrolyte solution is used together with solid electrolytic material such as conductive polymer, because the electrolyte solution is excellent in recovery action at a failure of the anodic oxide film working as dielectric.
FIG. 4 is a sectional view illustrating a structure of a conventional hybrid electrolytic capacitor (wound type), and FIG. 5 is an exploded perspective view of a capacitor element of this hybrid electrolytic capacitor. FIG. 6 is a sectional view illustrating schematically an essential part enlarged.
As shown in FIG. 4, this hybrid electrolytic capacitor comprises the following elements: capacitor element 2 as a functional element, a pair of lead wires 1A, 1B, and outer package 5. First ends of lead wires 1A, 1B are connected to capacitor element 2, and second ends thereof are led outside. Outer package 5 encloses capacitor element 2 and electrolyte solution (not shown) together therein.
As shown in FIG. 5 and FIG. 6, capacitor element 2 includes anode foil 2A, cathode foil 2B, and separator 2C. Anode foil 2A is made of foil of valve metal, e.g. aluminum, having undergone an etching process to roughen the surface, on which dielectric layer 2E of the anodic oxide film is formed by a chemical conversion process. Cathode foil 2B is made of valve metal such as aluminum. Anode foil 2A and cathode foil 2B are layered and wound together with separator 2C disposed therebetween.
On top of that, conductive polymer layer 6 formed of particles or aggregate of the conductive polymer such as polyethylene dioxythiophene is disposed between anode foil 2A and cathode foil 2B. This polymer layer 6 is provided on the surfaces of anode foil 2A, cathode foil 2B, and separator 2C. First ends of lead wires 1A, 1B are connected to anode foil 2A and cathode foil 2B respectively, and second ends thereof are led out from the same end face of capacitor element 2.
Outer package 5 is formed of cylindrical housing 3 having a bottom, and sealer 4. Housing 3 accommodates capacitor element 2 impregnated with electrolyte solution. Sealer 4 includes through holes 4A, 4B for lead wires 1A, 1B to run through respectively. Sealer 4 is disposed at an opening of housing 3, and a drawing process is provided to an outer wall of housing 3 to compress and deform the opening, thereby sealing the opening with the aid of sealer 4 formed of rubber packing.